DESCRIPTION: Each year millions of respiratory allergies and infections are caused by airborne microorganisms present in agricultural, industrial and indoor environments. The level of exposure indicated by bioaerosol samplers depends on the instrument used and the sensitivity of the microorganisms. In an effort to collect such microorganisms more gently, at low power and at minimal pressure drop, an electrostatic sampling technique has been developed and evaluated in the laboratory under the present NIOSH grant. As a major part of this development, an electrostatic particle-size classifier and a microorganism dispersion device with optional induction charging were developed to study the electric charges on airborne microorganisms. It has experimentally been proven that laboratory-dispersed indoor air bacteria, such as Pseudomonas fluorescens, had a net negative charge. Some of the bacteria were found to carry several thousand negative or positive charges. In contrast, particles of non-biological origin were found to carry very few positive or negative charges. This finding suggests that the electrostatic sampler will be capable of retaining airborne microorganisms by its electrostatic collecting field without first charging the microorganisms in the inlet section, thus reducing the complexity and power consumption for sampling in occupational environments. During the two years of the proposed grant continuation, this discovery will be evaluated in the laboratory with common bacteria and fungal spores and in the field through sampling of (1) microorganisms present in indoor air environments, (2) liquid-borne microorganisms in metalworking fluid environments, and (3) high concentrations of airborne microorganisms in agricultural environments. The physical and biological collection efficiencies will be determined from the relationship between the total and viable microorganisms collected by the new sampler and the number of uncollected microorganisms passed through the new sampler and collected by other means. The testing will indicate under what release conditions the microorganisms are sufficiently charged for collection by the simplified version of the new sampler. Microorganisms dispersed by mechanical action are expected to carry a particularly high charge and to be collected very efficiently by the electrostatic sampler without having to charge them in the inlet section. The new method will be used in occupational environments where airborne microorganisms are naturally present or are released by industrial processes.